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BCH1048 Tutorial 8 - Why do large animals need a...

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Unformatted text preview: Why do large animals need a circulatory system? • Diffusion – is too slow to keep up with respiration and effectively move materials over distances larger than a few cell diameters. The circulatory system connects with all body tissues with – Capillaries ( • – m ¸ b ) • Sites of exchange between blood and interstitial fluid blood interstitial • Have a relatively large surface area for exchange large Capillary Wastes Interstitial fluid Tissue cell O2 Nutrients Diffusion of molecules Different internal transport systems evolved in animals evolved • Gastrovascular cavity – E.g. hydra, jellyfish • Open circulatory system Open – E.g. insect • Closed circulatory system Closed – E.g. earthworm, fish, human Gastrovascular cavity of a hydra Gastrovascular Gastrovascular Gastrovascular cavity cavity Open and closed circulatory systems Open RG Õ D R h– b hm b– CG Open circulatory system Closed circulatory system Open circulatory system in a grasshopper • Circulatory fluids – Blood (always contained within blood vessels) – Hemolymph • – m (flows into a body cavity b called a hemocoel • – ) b • Hemolymph is seen in animals that have an open circulatory system. Open circulatory system in a grasshopper • Heart pumps hemolymph via vessels into tissue, and, eventually, hemolymph drains back to the heart. Open circulatory system in a Open grasshopper • When the heart contracts, opening called ostia h – (sing., b ostium) are closed. • When the heart relaxes, the hemolymph is sucked back into the heart by the way of the ostia. What is the color of hemolymph of a grasshopper? Transport in birds & Transport mammals mammals Heart Vein Artery h b– h b– Venule Arteriole hm b– h– m b Precapillary sphincter b– ( m¸ª Capillaries h– m¸ b Artery Artery Thick wall Able to expand and Able accommodate the sudden increase in blood volume that results after each results heartbeat Arterioles Capillary Capillary Red blood cells pass Red through in single file, allow exchange of nutrients & wastes across their thin wall wastes Microscopic, Microscopic, one cell-thick one Vein Vein Wall is thinner than Wall that of an artery that Lower blood pressure in the veins; Valves point toward the heart, Valves preventing a backflow of blood when they close. they Comparison of circulatory pathways Comparison h b– h b– hm b– One-circuit system • The heart has a single atrium atrium ( h – ) and ventricle ( h – ) and b ventricle b pumps the blood into the gill, where gas exchange occurs. • Disadvantage: – Blood pressure created by the heart pumping is reduced after the blood passes through the gill capillaries. Two-circuit system • The heart pumps blood to: – systemic circuit (tissues) – pulmonary circuit (lungs) pulmonary • In amphibians and reptiles, the heart pumps blood to BOTH the pulmonary capillaries and the systemic capillaries. • The heart has 2 atria and 1 ventricle. • Disadvantage? Two-circuit system • In birds, crocodiles and mammals, the pulmonary and systemic circuits are completely separate. • The heart is divided by a septum ( h – ) into right and left septum b halves. • The right side pumps blood to the lungs, and the left side pumps blood to the rest of the body. The mammalian heart • The heart is a double pump. double • The right ventricle of the heart sends blood into the pulmonary circuit. pulmonary • The left ventricle sends blood into the systemic circuit. circuit. • Since the left ventricle has the harder job of pumping blood to the entire body, its walls are thicker than those thicker of the right ventricle. Right atrium Semilunar valve Atrioventricular (AV) valve Left atrium Semilunar valve AV valve Right Left ventricle ventricle A cardiac cycle cardiac Heart is relaxed, atrioventricular (AV) valves are open. Atria contract to push blood into the ventricles. Systole ( h – m ¸ Systole b ) 0.1 sec Diastole ( h m ¸ b– ): ): 0.4 sec 0.3 sec Blood flows from the veins into the heart chambers Ventricles contract and semilunar valves are open to propel blood into the large arteries ...
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